Gas discharge transmission arrangement



J1me 1953 L. GOLDSTEIN ET AL GAS DISCHARGE TRANSIMISSION ARRANGEMENTFiled Dec. 3, 1948 Patented June 23, 1953 GAS DISCHARGE TRANSMISSIONARRANGEMENT Ladislas Goldstein, Weehawken, and Nathaniel L. Cohen,'Teaneck, N. J., assignors to Federal Telecommunication Laboratories,Inc., New :YOrk, N. Y., a corporation of Delaware Application December3, 19,48, Serial No. 63,284

13 Glaims. 1

This invention relates to radio frequency transmission systems and moreparticularly to systems employing a gas discharge tube as a radiofrequency transmission line element.

It has been proposed heretofore to employ a gas plasma set up within agaseous discharge tube to convey radio frequency wave energy betweenelectrodes immersed in the gas. However when the electrodes of the tubeare energized by a low frequency alternating current, or by directcurrent, the radio frequency conductivity or transmission characteristicof the gas plasma may not be all that is desired. According to thepresent invention, the radio frequency conductivity and wavetransmission characteristics of the gas plasma are increased by usingthe light quanta generated in the plasma to control thephoto-conductance or photo-electron-emissive properties of a coating orcoatings applied to the gas tube.

Therefore, one of the principal objects of this invention is to improvethe radio frequency conductive properties and wave transmissioncharacteristics between electrodes immersed in an ionizable mediumcapable of setting up a gas plasma therein.

Another object is to provide a novel radio frequency wave transmissionline of the coaxial type, wherein the center conductor is composed inpart at least, of a gas plasma.

A feature of the invention relates to a gaseous discharge tube having atleast part of its wall surface provided with a photo-emissive materialwhich responds to the light energy developed in the plasma, to enhancethe radio frequency conductivity between the tube electrodes;

Another feature of the invention relates to a gaseous discharge tubeprovided with a coating of a material which increases its electricalconductance in response to incident light energy produced in the gasdischarge plasma within the tube.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be bestunderstood-by reference to the following descriptionof an embodiment of the invention taken in conjunction-with theaccompanying drawings, wherein:

Fig. 1 illustrates one embodiment of-the invention.

Fig. 2 illustrates another embodiment of the invention.

It is known that when an ionizable medium such as a gas contained withina bulb or envelope is subjected to suitable ionizingpotentials, there isset up within the medium a plasma or region that contains substantiallyequal numbers of positive ions and electrons in "addition to gasmolecules. It isalso known that in such a gas discharge plasma, there isa large emission of photonsor light energy quanta. It is also known thatin such a plasma there is alarge ambipolar diffusion current resultingfrom a diffusion of the electrons to the walls of the tube. Since thisdiffusion normally represents a loss of electrons from the gas dischargeplasma, the capability of the plasma to act as a radio frequencytransmission line element or link is correspondingly reduced. -In orderto overcome this drawback, the present invention provides either on theinterior wall of the tube or on the exterior wall thereof, or on bothwalls, a coating of a material which may be either photo-emissive inresponse to incident photons, or which increases its electricalconductance in response to incident photons. In accordance with theinvention, this increase in electron emission or electric conductance ofthe coating is controlled by the photons which are emitted from the gasdischarge plasma itself.

The invention is particularly useful where the gas discharge plasmaforms .part of the central conductor of a coaxial wave transmissionline, although in its broad aspects the invention is not necessarilylimited to that particular field of use.- fulness.

Merely for illustration, therefore, there is shown in Fig. 1 of thedrawing a coaxial wave trans mission line embodying the invention. Inthisfigure the block i represents any well-known source of radiofrequency wave energy, and the block *2 represents any well-known radiofrequency load device or terminal equipment to which the radio frequencyenergy is to be transmittedfrom source I. The source I is connected tothe equip-ment 2 by a coaxial wave transmission line havingan outer orhollow pipe conductor 3 and a central or inner conductor 4. Preferably,although not necessarily, the conductor 4 is also in the form of ahollowpipe. The pipe 4 has a gap between its ends-and this gap is bridged by agaseous discharge tube 5. The tube 5 is of glass and is approximately ofthe same outside diameter as theinside diameter of pipe conductor 4.Sealed through theleft-hand end of tube 5 is a lead-in conductorfi towhich is attacheda cuplike cathode 1. The right-hand end of tube 5 issealed to a metal cap anode 8. The tube 5, after being suitablyevacuated and processed as is well-known in the gaseous conduction tubeart, is provided with a filling of a suitable ionizable medium such asgas or vapor. Preferably this filling consists oi? an inert gas such asneon, argon, krypton, helium, and the like, or a mixture thereof, at asuitable predetermined pressure. The left-hand end of tube 5 is providedon the exterior thereof with a metal or other conductive coating 9surrounding the region of the cathode i. The left-hand end of the tubeis adapted to be telefscoped within the open end of the conductor 4, andif desired, the said conductor 4 may be of flexible thin-walledconstruction, as indicated by the numeral I4, so as to provide a goodelectrical contact with the coating 9. Likewise the cap 8 is telescopedwith the corresponding section of conductor l so as to provide a goodelectrical contact therewith.

In accordance with one feature of the invention, the greater part of thelength of the tube 5 has on its interior surface a coating I of anywell-known material which emits photo-electrons in response to impinginglight energy, such as those conventionally employed inphoto-electriccells such for example as sodium, potassium, and the like. In accordancewith the invention, this light energy is produced by the gaseous fillingwithin the tube 5, and for this purpose-the cathode i can be connectedto the negative terminal of a suitable D. C. voltage supply, and the cap8 which forms the anode, can be connected to the positive terminal ofthis or any other D. C. voltage supply. In accordance with thewell-known operation of gaseous discharge tubes, by applying anappropriate voltage across the electrodes 7 and 8, there is set upwithin the tube a gaseous discharge plasma which contains a highintensity of photons or light energy quanta. It is also known that insuch a plasma there is a large ambipolar diffusion current. Ordinarilysuch difiusion would represent a loss of electrons to the gas dischargeplasma. However, by providing the light-responsive electron-emissivecoating it, the light energy from the plasma which strikes this coatingis absorbed and photo-electrons are released from the coating anddirected toward the axis of the tube to counteract the loss ofconductivity. This action provides a more efilcient radio frequencyenergy conduction path between the sections of the line conductor 4which is bridged by the tube 5. Probably one explanation for this isthat the electrons which are normally bound to the atoms of the coatingmaterial, be-

come energized by the light energy from the gas discharge plasma, andthey are then free to move with very high mobility through the plasmatowards the anode 8, thus increasing the conductivity of the tube. Whilethe gaseous conduction medium has normally a certain amount ofconductivity, its conductivity is greatly increased or supplemented bythe photo-emission from the coated surface 5 when excited by the lightenergy from the plasma.

Preferably a radio frequency choke coil H is connected between thecathode l and the ionizing potential source, so that the radio frequencyenergy from the source I passes from the line conductor 5 and cOating 9,and thence by capacitive coupling, to the cathode 7. As a result of theenhanced conductivity of the tube 5 as above mentioned, this radiofrequency energy passes through the gas plasma within the tube 5 to theanode 3, line conductor 4' and thence to the radio frequency load 2.

It will be understood, of course, that the invention is not necessarilylimited to the use of a 4 D. C. ionizing potential on the electrodes 1and 8, and if desired a suitable low frequency alternating currentsource may be used for that purpose.

From the foregoing description it will be seen that the tube 5 with itsgas plasma, forms in effect a continuity of the central conductor 4 ofthe coaxial wave transmission line. It will be understood, of course,that the tube 5 can be used in any other system wherein it is desired toincrease the conductivity of the tube between the electrodes thereof.

Fig. 2 shows a modification of Fig. l, and the elements of Figs. 1 and 2which are structurally and functionally the same, are designated alike.The essential difference between the embodiment of Fig. 2 and. that ofFig. l, is that in Fig. 2 the light responsive coating 12 on theinterior of tube 5, instead of being of a character which emitsphoto-electrons in response to incident light energy, is of a type Whichincreases its electric conductance in response to incident light energy.An example of such material is selenium. In Fig. 2, as in Fig. l, thecoating extends along the greater part of the length of the internalsurface of the tube 5, but terminates short of the cathode 1 and theanode 8. If desired, the outer surface of the tube 5 can be providedwith a similar coating 53 of a material like the coating 52. When thegaseous medium within the tube 5 is ionized as above described, it setsup a gaseous discharge plasma, and the light energy from this plasmaacts on the coatings i2 and i3 to increase their conductivity, thusproviding a more efficient radio frequency conduction path between thesections of the center line conductor l.

It will be understood, of course, that if desired, the coating which isused to increase the radio frequency wave energy conductivity, mayconsist of a combination of a light-responsive electronemissivematerial, and a light-responsive material which increases itsconductivity.

While we have described above the principles of our invention inconnection with specific ap= paratus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of our invention.

What is claimed is:

l. A gaseous discharge device comprisin an enclosing envelope having :afilling of an ionizable medium, a pair of spaced electrodes forinitiating and sustaining a gaseous discharge plasma within said medium,and a coating of light-responsive electron-emissive material on the wallof said envelope in the space between said electrodes, but conductivelyisolated from said electrodes, for increasing the conductivity of theplasma.

2. A gaseous dischargedevice comprisin an enclosing envelope having afilling of an ionizable medium, a pair of spaced electrodes forinitiating and sustaining a gaseous discharge plasma within said medium,and a coating, on the wall of said envelope in the space between saidelectrodes, but conductively isolated from said electrodes, of amaterial which changes its electrical conductance in response toincident light energy derived from the discharge plasma for increasingthe electrical conductivity between asid electrodes.

3. A gaseous discharge device comprising an enclosing envelope ofinsulating material, said envelope having a filling of an ionizablemedium, a pair of spaced electrode within said envelope, a coating oflight-responsive electron-emissive material on the inner wall of saidenvelope in the space between said electrodes but conductively isolatedfrom said electrodes, said electrodes adapted to initiate and sustain agaseous discharge plasma therebetween upon application thereacross of apotential from an ionizing source and to excite said coating by photonsderived from such discharge plasma to increase the high frequencyelectrical conductivity of the space between said electrodes.

4. A gaseous discharge device comprising an enclosing envelope ofinsulating material, said envelope having a filling of an ionizablemedium, a pair of spaced electrodes Within said envelope, a coating, onthe inner wall of said envelope in the space between said electrodes butconductively isolated from said electrodes, consisting of a materialwhich increases its electric conductivity in response to incident lightenergy, said electrodes adapted to initiate and sustain a gaseousdischarge plasma therebetween upon application thereacross of apotential from an ionizing source, thereby to excite said coating byphotons to increase the high frequency electric conductivity of thespace between said electrodes.

5. A radio frequency transmission line conductor having two endsdefining a gap therebetween, a gaseous discharge tube coupled betweenthe two ends of said conductor defining said gap, said tube having apair of spaced electrodes therein, means to energize said electrodes toinitiate a gaseous discharge plasma, said tube having on the wallthereof in the space between said electrodes a coating oflight-responsive material for altering the radio frequency conductivitybetween said electrodes.

6. A coaxial wave transmission line adapted to couple a source of highfrequency energy to a utilization circuit comprising an outer hollowconductor, an inner central conductor having two ends defining a gaptherebetween, a gaseous discharge tube connected between the two ends ofsaid conductor defining said gap, said tube having a pair of spacedelectrodes adapted to be coupled to a source of ionizing potential, saidelectrodes adapted to initiate and to sustain a gaseous discharge plasmatherebetween, a coating of light-responsive material on the wall of saidtube in the space between said electrodes for increasin the highfrequency conductivity of the plasma in response to the light energyderived therefrom, and means to isolate said sources from each other.

7. A coaxial wave transmission line as claimed in claim 6, wherein saidelectrodes are disposed at opposite ends of said tube and said isolationmeans comprises a capacitive coupling between one of said electrodes andthe central conductor of said coaxial line.

8. A coaxial wave transmission line as claimed in claim 6, wherein saidisolation means further comprises an inductive impedance seriallyconnected in the ionization discharge path of said tube.

9. A radio frequency transmission line comprising a metal line conductorhaving two ends defining a gap therebetween, a gaseous discharge tubehaving an envelope of transparent, insulating material, said tubedisposed across the two ends of said conductor definin said gap, saidtube having a pair of electrodes within said envelope at opposite endsthereof, said electrodes adapted to be coupled to a source of ionizingpotential and to initiate and to sustain a gaseous discharge plasmatherebetween, a first coating of a photo conductive material on theexterior of said envelope, said material electrically insulated fromeach of the ends of said conductor defining said gap, a second coatingof a light-responsive material on the inner wall of said envelopeelectrically insulated from each of said electrodes, whereby the lightenergy derived from the discharge plasma acts on both of said materialcoatings to increase the radio frequency conductivity thereof.

10. A radio frequency transmission line according to claim 9 in whichboth coatings on said envelope are of a light-responsive electronemissive material.

11. In combination, a radio frequency transmission line conductor havingtwo ends thereof defining a gap therebetween, a gaseous discharge tubehaving an enclosing envelope with a filling of an ionizable medium, apair of spaced electrodes Within said envelope at opposite ends thereof,said electrodes adapted to be coupled to a source of ionizing potentialand to initiate and to sustain a gas discharge plasma therebetween, saidenvelope having a coating of light-responsive material in the spacebetween said electrodes, which material responds to light energy derivedfrom said plasma, said tube disposed across the two ends of saidconductor defining said gap, means to couple radio frequency energy fromsaid line conductor into said plasma, said lightresponsive materialadapted to enhance the radio frequency conductivity between the two endsof said conductor defining said gap.

12. A combination according to claim 11, in which said ionizingpotential is a D. 0. potential.

13. A combination according to claim 11, in which said ionizingpotential is a low frequency potential.

LADISLAS GOLDSTEIN. NATHANIEL L. COHEN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,955,335 Knowles Apr. 1'7, 1934 2,229,135 Schade Jan. 21,1941 2,258,472 Ruttenauer et a1. Oct. 7, 1941 2,259,040 Inman Oct. 14,1941 2,351,895 Allerding June 20, 1944 2,412,659 Thomas Dec. 17, 19462,438,873 McCarthy Mar. 30, 1948

